Explanation:

- We need to find the average age of all the girls in the class.

- The class has two groups: 25 girls with an average age of 11.2 years and 15 girls with an average age of 10 years.

- Calculate total age for each group:

- First group: 25 girls × 11.2 years = 280 years

- Second group: 15 girls × 10 years = 150 years

- Combine total age: 280 years + 150 years = 430 years.

- Find total number of girls: 25 + 15 = 40 girls.

- Calculate the average age of all the girls: 430 years ÷ 40 girls = 10.75 years.

- Option 1: 10.75 years is the correct answer

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